[Gllug] Wireless access point/ADSL Modem/Router

[Chris Bell]

On Wed 28 Apr, John Hearns wrote:
> 
> On Wed, 2004-04-28 at 08:50, Chris Bell wrote:
> 
> >    I do not know whether it has changed since, but on the digital techniques
> > course I attended many years ago I was told that, in the BT ATM system,
> > routeing information went ahead of the data,
> ATM cells (not packets) are not routed. They are switched via permanent
> virtual circuits or switched virtual circuits.
> 
> 
   Which still involves high speed switching, perhaps for a standard number
of individual ATM cells sent at regular intervals as a group, which would
explain the previously recommended temporary MTU of 1458 for ethernet
packets. Stream re-routeing does happen, and it used to cause total loss of
analogue broadcast video carried over ATM if the switching rate between
different routes was excessive, with variable transit delays. Internet data
and digital television can be simply delayed as late packets catch up, but
we are sensitive to small delays in analogue communication. There is a
variety of cross country links, capable of different data rates, so data
streams are multiplexed together, but both large and small streams still
need to be compiled and separated at various stages. I think that my ADSL
box would be a little confused if it was asked to select anything relevant
from one of the data streams sent to my local exchange.

-- 
Chris Bell

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